Shared fantasy and especially idealization defense against triggering of early childhood traumas (hurt aversion, dread of intimacy and love): she is ideal, so will not hurt me, I am perfect, so above reproach and invulnerable.
Recreates secure base and symbiosis (back to womb).
Shared fantasy differs from infatuation and limerence:
Anomic (antisocial)-rigid delusional kingdom
Intensity (controlled dysregulation, like addiction)